1. Field of the Invention
The invention relates to error detecting and correcting methods and apparatuses, particularly for bubble memories.
2. Prior Art
During the reading, writing and shifting of binary data in a magnetic bubble memory, a predictable number of bubbles either slip in position or disappear. This, of course, results in loss or distortion of the stored data. These failures, with current state-of-the-art bubble memories, are random and moreover, not attributable to identifiable circuit defects. They occur more frequently when the memory is operated near its maximum or minimum operating temperature. Memory start-up and shut-down, in addition to bubble shifting (e.g. data circulation) increases the chances of such failures. In a 256K memory under normal operating conditions, one failure every few operating hours is well within the order magnitude of expected failures. These failures, however, will increase markedly at high or low temperatures, several thousand times this normal operating failure rate may occur at operating temperature extremes.
Cyclic codes for detecting errors in binary data and for permitting the correction of such errors have been known for a number of years. For example, such codes are discussed in "Cyclic Codes for Error Detection" by W. W. Peterson and D. B. Brown, Proceedings of the I.R.E., January, 1961, beginning at page 229. Such codes are typically used to correct data as blocks of data are read from a memory into a system. These codes are also used to encode data for transmission, particularly over long distances, to permit the detection and correction of errors which result from the sensing of low level signals.
The present invention expands upon the use of error correcting codes. A code is used in the present invention to periodically repair data in memory as will be described in greater detail.